This invention relates generally to gas turbine engines and, more particularly, to fuel delivery systems for fuel nozzle staging for gas turbine engines.
Controlling a pressure ratio of fuels delivered to a dual fuel gas turbine engine is critical for the engine""s performance. Typically, dual fuel gas turbine engines exhibit operability limitations during normal engine starts and during engine low power operating conditions. For example, undesirable engine flameouts are prevalent in gas turbine engines supplied with gas and steam premix, or dual fuel (gas and liquid), and in steam premix turbines as a result of the low fuel flow rates supplied during start conditions. Additionally, flameouts may occur at steady state fuel flow conditions in gas turbine engines when low pressure differentials develop at the fuel nozzle tips, i.e., single annular combustor (SAC) fuel configuration.
To compound the flammability problem, typically the performance of gas turbine engine fuel delivery systems are optimized to be within acceptable performance ranges when the gas turbine engines are operating at maximum fuel flow conditions. While optimizing a fuel delivery system to perform at maximum fuel flow conditions enhances the performance of the gas turbine engine during high fuel flow conditions, it also increases the possibility of flameouts during low fuel flow conditions. Fuel nozzle pressures can be raised to alleviate flammability operability regions of the engine. However, raising the fuel nozzle pressures to improve the flammability levels at low fuel flow conditions may cause excessive and damaging pressures at maximum fuel flow conditions, where the engine operates more frequently. Additionally, optimizing the fuel delivery systems at low fuel flow conditions may increase carbon monoxide emission levels generated by the gas turbine engine, thus creating potential environmental issues.
In an exemplary embodiment, a fuel delivery system for fuel nozzle staging is provided for use with a gas turbine engine. The fuel delivery system includes two circuits. A gas circuit delivers fuel to the gas turbine engine, and includes a primary manifold and a secondary manifold. A steam circuit delivers steam to the gas turbine engine and includes a primary manifold and a secondary manifold. Both the gas circuit and the steam circuit are connected to a plurality of fuel nozzles which include primary fuel nozzles and secondary fuel nozzles. Additionally, both circuits include a staging valve to control the flow of each respective gas and steam into each respective circuit""s second manifold.
During operation, the gas circuit primary manifold and the steam circuit primary manifold deliver fuel and steam respectively to the gas turbine engine during initial operation and idle operation of the gas turbine engine. During initial operations and idle operations, the primary fuel nozzles deliver the first fuel and steam to the gas turbine engine. Once the gas turbine engine reaches a predetermined operational speed, the staging valves open and direct fuel and steam into the secondary fuel nozzles. As a result of such fuel nozzle staging, the fuel and control system eliminates more detrimental fuel delivery systems and provides a user with a fuel delivery system which improves flammability limits, accurately controls the delivery of fuel, and provides flexibility to the user.